https://github.com/webcompat/web-bugs/issues/39773

scroller.js

(function ($) {
  var height = $.fn.height,
  width = $.fn.width,
  left = $.fn.left,
  top = $.fn.top;
  $.fn.extend({
    width: function () {
      if (!this[0]) error();
      if (this[0] == window) return self.innerWidth || $.boxModel && document.documentElement.clientWidth || document.body.clientWidth;
      if (this[0] == document) return ((document.documentElement && document.compatMode == 'CSS1Compat') ? document.documentElement.scrollWidth : document.body.scrollWidth);
      return width.apply(this, arguments)
    },
    height: function () {
      if (!this[0]) error();
      if (this[0] == window) return self.innerHeight || $.boxModel && document.documentElement.clientHeight || document.body.clientHeight;
      if (this[0] == document) return ((document.documentElement && document.compatMode == 'CSS1Compat') ? document.documentElement.scrollHeight : document.body.scrollHeight);
      return height.apply(this, arguments)
    },
    left: function () {
      if (!this[0]) return true;
      var obj = document.getElementById ? document.getElementById(this[0].id)  : document.all(this[0].id);
      var tagCoords = new Object();
      tagCoords.x = obj.offsetLeft;
      while ((obj = obj.offsetParent) != null) {
        tagCoords.x += obj.offsetLeft
      }
      if ((tagCoords.x * 0) == 0) return (tagCoords.x);
       else return (this[0].id)
    },
    top: function () {
      if (!this[0]) return true;
      var obj = document.getElementById ? document.getElementById(this[0].id)  : document.all(this[0].id);
      var tagCoords = new Object();
      tagCoords.y = obj.offsetTop;
      while ((obj = obj.offsetParent) != null) {
        tagCoords.y += obj.offsetTop
      }
      if ((tagCoords.y * 0) == 0) return (tagCoords.y);
       else return (this[0].id)
    }
  })
}) (jQuery);
$(function () {
  $('a[href^="#"], area[href^="#"]').not('.nopscr a[href^="#"], a[href^="#"].nopscr').click(function () {
    var usrUrl = location.hostname + location.pathname;
    var anchorPath = ((this.href).substring(0, (((this.href).length) - ((this.hash).length)))).slice((this.href).indexOf('//') + 2);
    if (usrUrl.lastIndexOf('?') != - 1) usrUrlOmitQ = usrUrl.slice(0, (usrUrl.lastIndexOf('?')));
     else usrUrlOmitQ = usrUrl;
    if (anchorPath.lastIndexOf('?') != - 1) anchorPathOmitQ = anchorPath.slice(0, (anchorPath.lastIndexOf('?')));
     else anchorPathOmitQ = anchorPath;
    if (anchorPathOmitQ == usrUrlOmitQ) {
      coliss.toAnchor((this.hash).substr(1));
      return false
    }
  });
  $('body').click(function () {
    coliss.stopScroll()
  })
});
this.pageScrollTimer = null;
var coliss = {
  getScrollRange: function (type) {
    if (type == 'x') return (($(document).width()) - ($(window).width()));
     else if (type == 'y') return (($(document).height()) - ($(window).height()))
  },
  getWindowOffset: function (type) {
    if (type == 'x') return (window.pageXOffset || document.body.scrollLeft || document.body.parentNode.scrollLeft);
     else if (type == 'y') return (window.pageYOffset || document.body.scrollTop || document.body.parentNode.scrollTop)
  },
  pageScroll: function (toX, toY, frms, frX, frY) {
    var pageScrollTimer;
    if (pageScrollTimer) clearTimeout(pageScrollTimer);
    var spd = 16 * adjSpeed;
    var actX = coliss.getWindowOffset('x');
    var actY = coliss.getWindowOffset('y');
    if (!toX || toX < 0) toX = 0;
    if (!toY || toY < 0) toY = 0;
    if (!frms) frms = $.browser.mozilla ? 10 : $.browser.opera ? 8 : 9;
    if (!frX) frX = 0 + actX;
    if (!frY) frY = 0 + actY;
    frX += (toX - actX) / frms;
    if (frX < 0) frX = 0;
    frY += (toY - actY) / frms;
    if (frY < 0) frY = 0;
    var posX = Math.ceil(frX);
    var posY = Math.ceil(frY);
    window.scrollTo(posX, posY);
    if ((Math.floor(Math.abs(actX - toX)) < 1) && (Math.floor(Math.abs(actY - toY)) < 1)) {
      clearTimeout(this.pageScrollTimer);
      window.scroll(toX, toY)
    } else if ((posX != toX) || (posY != toY)) this.pageScrollTimer = setTimeout('coliss.pageScroll(' + toX + ',' + toY + ',' + frms + ',' + frX + ',' + frY + ')', spd);
     else clearTimeout(this.pageScrollTimer)
  },
  stopScroll: function () {
    clearTimeout(this.pageScrollTimer)
  },
  cancelScroll: function (e) {
    coliss.stopScroll()
  },
  toAnchor: function (idName) {
    coliss.stopScroll();
    var anchorX,
    anchorY;
    if (!!idName) {
      if (idName == virtualTopId) {
        anchorX = (virtualTop == 0) ? 0 : (virtualTop == 1) ? window.pageXOffset || document.body.scrollLeft || document.body.parentNode.scrollLeft : $('#' + idName).left();
        anchorY = ((virtualTop == 0) || (virtualTop == 1)) ? 0 : $('#' + idName).top()
      } else {
        anchorX = (adjTraverser == 0) ? 0 : (adjTraverser == 1) ? ($('#' + idName).left())  : window.pageXOffset || document.body.scrollLeft || document.body.parentNode.scrollLeft;
        anchorY = adjPosition ? ($('#' + idName).top()) + adjPosition : ($('#' + idName).top())
      }
      var dMaxX = coliss.getScrollRange('x');
      var dMaxY = coliss.getScrollRange('y');
      if (((anchorX * 0) == 0) || ((anchorY * 0) == 0)) {
        var setX = (anchorX < 1) ? 0 : (anchorX > dMaxX) ? dMaxX : anchorX;
        var setY = (anchorY < 1) ? 0 : (anchorY > dMaxY) ? dMaxY : anchorY;
        coliss.pageScroll(setX, setY)
      } else location.hash = idName
    } else coliss.pageScroll(0, 0)
  },
  initPageScroller: function () {
    var usrUrl = location.href;
    var checkAnchor = usrUrl.indexOf('#', 0);
    var checkPageScroller = usrUrl.match(callExternal);
    usrUrl = usrUrl.replace(/</g, '&lt;');
    usrUrl = usrUrl.replace(/>/g, '&gt;');
    if (!!checkPageScroller) {
      anchorId = usrUrl.slice(usrUrl.lastIndexOf('?' + callExternal) + 4, usrUrl.length);
      timerID = setTimeout('coliss.toAnchor(anchorId)', delayExternal)
    }
    if (!checkAnchor) window.scroll(0, 0);
     else return true
  }
};
$(coliss.initPageScroller);